1. Technical Field
This invention relates to a water-cooled heat-accumulating type drink cooling system for use in cup-type automatic vending machines for refreshing drinks and dispensers for cold water or refreshing drinks.
2. Description of the Prior Art
In water-cooled heat-accumulating type drink cooling systems, a cooling water tank is filled with water and a cooler is submerged in the water tank which consists of an evaporator for a refrigerator, a drink cooling coil formed at an intermediate portion of a drink supply pipeline, and an electric water agitator. The water in the tank is cooled by the refrigerator and stirred by the agitator, and serves as a heat transfer medium for a drink flowing in the drink cooling coil. In order to minimize the cooling capacity requirements of the refrigerator, an ice layer, also referred to as an ice bank, is always maintained aound the cooler disposed in the water tank. Accordingly, even when the operation of the refrigerator is interrupted, the cooling water in tank can be maintained at a low temperature due to the heat being absorbed by the ice bank. The above described method of momentarily increasing the drink cooling capacity is widely utilized. However, this conventional method has significant disadvantages, as will be described.
When a drink supply instruction is given in this conventional drink cooling system operated in accordance with the above-described method, oftentimes the drink or beverage in the drink supply pipeline becomes clogged in the line even though the pump and supply valve are operating normally. It has been found that this clogging of the drink flow is caused by small pieces of ice forming and gathering in narrow portions of the drink supply pipe-line and inner portions of the supply valve. It has been further determined that the cause of small pieces of ice forming and gathering is apparently because the drink in the drink cooling coil is over-cooled and partly frozen. The reason for the clogging will become more apparent with a more detailed description of the operation of the prior art circuit, which follows.
During an initial stage of the formation of the ice bank on the surface of the cooler, the water in the tank is first over-cooled to a negative temperature of T.sub.o .degree.C., which is lower than 0.degree. C., i.e. the freezing point of water. In order for ice to be formed on the surface of the cooler, it is generally necessary that the water around the surface of the cooler be initially over-cooled to a temperature below 0.degree. C. However, soonafter the temperature of the water has been decreased to below 0.degree. C., ice begins to form and the temperature of the water becomes 0.degree. C. Once an initial layer of ice is formed on the surface of the cooler, the ice layer grows continuously in the outward directon. Consequently, due to the continuous operation of the cooler, only the temperature of the surface of the cooler, which is covered with a layer of ice, is maintained at a low level, and over-cooling does not occur in that part of the water in the tank which is not immediately proximate to the surface of the cooler.
When an agitator is continuously operated to stir the water in the tank, the temperature of the water is virtually equal in all parts of the tank, which temperature is substantially equal to that of the cooler. As a result, during the period when ice is being initially formed, an over-cooling phenomenon occurs not only in the water immediately around the cooler but also in the water in the remaining portion of the interior of the tank not immediately proximate to the cooler surface. This over-cooling temperature T.sub.o .degree. C. is approximately -0.5.degree. C. to -2.0.degree. C., although it varies depending upon the construction of the water tank, the capacity of the refrigerator and the operational condition of the agitator. Accordingly, when an over-cooling phenomenon occurs without a drink supply instruction given, the drink in the cooling coil is also over-cooled to a temperature below the freezing point, i.e., 0.degree. C., even though the cooling coil is not immediately proximate to the cooler. As a result, small pieces of ice in the pipeline will collect in narrow portions thereof and particularly in an inner portion of the supply valve. The end result is that the flow of drinking water is either blocked, or at the least, the drinking water is not supplied normally.
Since the quantity of drink in an automatic vending machine is normally controlled by controlling the time that the supply valve is opened, a clogging of ice as described above would result in an improper quantity of dispensed drink, which of course would be undesirable. While in the above description the particular fluid being cooled and supplied is drinking water, it should be understood that when syrup or other kinds of drinks are cooled and supplied, a similar over-cooling problem would also likely occur.